Use expression with a variable r

问题

I am trying to label a plot with the following label:

"Some Assay EC50 (uM)" where the "u" is a micro symbol.

I currently have:

assay <- "Some Assay"
plot(0,xlab=expression(paste(assay," AC50 (",mu,"M)",sep="")))

But that gives: "assay EC50 (uM)" rather than the desired "Some Assay EC50 (uM)".

Suggestions? Thanks.

I also tried:

paste(assay,expression(paste(" AC50 (",mu,"M)",sep="")),sep="")

回答1:

You want a combination of bquote() and a bit of plotmath fu:

assay <- "Some Assay"
xlab <- bquote(.(assay) ~ AC50 ~ (mu*M))
plot(0, xlab = xlab)

The ~ is a spacing operator and * means juxtapose the contents to the left and right of the operator. In bquote(), anything wrapped in .( ) will be looked up and replaced with the value of the named object; so .(assay) will be replaced in the expression with Some Assay.

回答2:

another option using mtext and bquote

plot(0,xlab='')
Lines <- list(bquote(paste(assay," AC50 (",mu,"M)",sep="")))
mtext(do.call(expression, Lines),side=1,line=3)

Note that I set the xlab to null in the first plot.

EDIT No need to call expression, since bquote will create an expression with replacement of elements wrapped in .( ) by their value. So a goodanswer is :

plot(0,xlab='')
Lines <- bquote(paste(.(assay)," AC50 (",mu,"M)",sep=""))
mtext(Lines,side=1,line=3)

回答3:

You also could try the poor man's approach:

assay <- "Some Assay"
plot(0, xlab = paste0(assay, " AC50 (µM)"))

It specifies the mu character directly rather than using expressions (and paste0 is just paste with sep = "").

回答4:

Using tidy_eval approach you could do

library(rlang)

assay <- "Some Assay"
plot(0,xlab=expr(paste(!!assay," AC50 (",mu,"M)",sep="")))

expr and !! are included in tidyverse, so you don't actually need to load rlang. I just put it there to be explicit about where they come from.

来源：https://stackoverflow.com/questions/15074127/use-expression-with-a-variable-r

标签

expression